hardhat-verify

Hardhat plugin to verify the source of code of deployed contracts.

Installation

This plugin is part of Viem Hardhat Toolbox and Ethers+Mocha Hardhat Toolbox. If you are using any of those toolboxes, there's nothing else you need to do.

To install this plugin, run the following command:

npm install --save-dev @nomicfoundation/hardhat-verify

In your hardhat.config.ts file, import the plugin and add it to the plugins array:

import { defineConfig } from "hardhat/config";
import hardhatVerify from "@nomicfoundation/hardhat-verify";

export default defineConfig({
  plugins: [hardhatVerify],
});

Usage

Verifying on Etherscan

You need to add the following Etherscan config in your hardhat.config.ts file

import { defineConfig } from "hardhat/config";

export default defineConfig({
  verify: {
    etherscan: {
      // Your API key for Etherscan
      // Obtain one at https://etherscan.io/
      apiKey: "<ETHERSCAN_API_KEY>",
    },
  },
});

We recommend using a configuration variable to set sensitive information like API keys.

import { configVariable, defineConfig } from "hardhat/config";

export default defineConfig({
  verify: {
    etherscan: {
      // Your API key for Etherscan
      // Obtain one at https://etherscan.io/
      apiKey: configVariable("ETHERSCAN_API_KEY"),
    },
  },
});

Run the verify task passing the network where it's deployed, the address of the contract, and the constructor arguments that were used to deploy it (if any):

npx hardhat verify --network mainnet DEPLOYED_CONTRACT_ADDRESS "Constructor argument 1"

Programmatic verification

You can also verify contracts programmatically by using the verifyContract function from the plugin:

import hre from "hardhat";
import { verifyContract } from "@nomicfoundation/hardhat-verify/verify";

await verifyContract(
  {
    address: "DEPLOYED_CONTRACT_ADDRESS",
    constructorArgs: ["Constructor argument 1"],
    provider: "etherscan", // or "blockscout", or "sourcify"
  },
  hre,
);

Note: The verifyContract function is not re-exported from the Hardhat toolboxes, so you need to install the plugin and import it directly from @nomicfoundation/hardhat-verify/verify.

Build profiles and verification

When no build profile is specified, this plugin defaults to production. However, tasks like build and run default to the default build profile. If your contracts are compiled with a different profile than the one used for verification, the compiled bytecode may not match the deployed bytecode, causing verification to fail.

To avoid this, make sure to build and verify using the same profile:

npx hardhat build --build-profile production
npx hardhat verify --network mainnet DEPLOYED_CONTRACT_ADDRESS "Constructor argument 1"

If you're using the verifyContract function programmatically through a script, pass the build profile when running it:

npx hardhat run --build-profile production scripts/verify.ts

How it works

The plugin works by fetching the bytecode in the given address and using it to check which contract in your project corresponds to it. Besides that, some sanity checks are performed locally to make sure that the verification won't fail.